1. Field of the invention
This invention relates to a workpiece transfer device of a grinding machine wherein a rotationally driven main shaft and a tailstock spindle hold a workpiece therebetween, and wherein shoes are utilized to support the workpiece so as to maintain the workpiece at a grinding position.
2. Description of the Prior Art
A conventional grinding machine which utilizes shoes as well as a rotationally driven main shaft and tailstock spindle to hold a workpiece is disclosed in Japanese Patent Application Gazette No. 48-36557. This publication discloses a workpiece holding device of a grinding machine wherein a disc plate is fastened to the end surface of a main shaft to rotationally drive a workpiece, and a plurality of work-holding devices, each of which comprises a pair of shoes for rotatably holding each workpiece. The pairs of shoes are disposed along the axis of the main shaft on a foundation of the grinding machine. A holding member having a holding surface opposed to the disc plate is connected to a cylinder device provided on an arm or a table such that the holding member is axially movable. Further, in this device, the main shaft and the holding member are linked to rotate synchronously, and the plurality of workpieces are held between the disc plate and the holding member such that they are movable only in the radial direction. With this construction, the plurality of workpieces can be ground simultaneously by rotating the plurality of workpieces as they are held together by the main shaft and the holding member.
The grinding machine equipped with this type of workpiece holding device has limited space to allow for removing workpieces after they have been processed since the workpieces are supported by shoes. Due to such space limitations, it is difficult to design a mechanism for mechanically holding workpieces to remove them from the grinding machine. It is thus necessary to devise a compact mechanism which requires little space within which to function.
To solve these problems, a suction pad employing vacuum pressure can be used to remove workpieces from the grinding position. This method enables reliable removal of workpieces even in a limited space. However, this creates another problem. That is, in the process of attracting the workpieces by suction, the suction pad is likely to absorb coolant and grinding chips and become clogged.
When removing finished workpieces, it is necessary to provide space for removing the workpieces by moving the tailstock spindle back and moving the grinding wheel away from the workpieces. This operation, however, results in a longer machining time and a decreased efficiency.